Most integrated circuits draw varying amounts of current from their power supplies, depending on operating conditions. For example, current supplied to a combined block of programming-mode bitline drivers for an embedded flash memory will vary depending upon the number of bits being programmed at any time. In most integrated circuits this is advantageous, since only as much current is drawn from the power supply as is needed, thereby minimizing power consumption.
However, the supply current variation may be problematic when data on a chip must be secured. Secure products contain confidential and encrypted internal data, including keys, which must not be revealed to unauthorized parties. Differential power analysis (DPA) is a technique in which a chip's supply current is monitored externally for data-dependent variations that may indirectly reveal the internal data within the chip. In order to provide a high degree of immunity against DPA attacks, it is desired that current variations at the power supply pin or pins be made substantially independent of the data-dependent current demand or load within the chip. If possible, this should be accomplished without increasing power consumption more than necessary.